The present invention relates to a camera comprising various load devices such as an automatic exposure device, an automatic film advancing device and an electronic flash which are powered by a source battery mounted in the camera, and a control device such as a microcomputer also powered by the source battery for controlling the load devices. Such a camera further comprises a detecting device for detecting an output voltage of the source battery in relation to a predetermined voltage level, and a second control device for prohibiting or permitting the first-mentioned control device to transmit control signals to the various load devices in response to a detection signal received from the detecting device. With a capacity reduction of the battery, the voltage applied to the first control device such as a microcomputer falls below a minimum operating voltage thereof. As a result, the first control device may output abnormal control signals to cause malfunctions of the various devices. This camera prevents such malfunctions with the detecting device and the second control device.
In the camera noted above, once the detecting device outputs a low-voltage detection signal, the second control device holds the first control device against transmitting the control signals to the load devices. As a result, the load devices are maintained inoperable. Generally, an indication that the battery capacity has reduced is given to the user through a display device provided on the camera. The user will then learn that the battery has run down and should be replaced with a new one. Even if such a display device is not provided, the fact that the load devices do not operate will suggest a battery failure to the user as the most probable cause. Thus, the battery is changed once the output voltage thereof falls below the predetermined level.
Furthermore, various photographic information necessary for photo-taking, such as film sensitivity information and photographing modes, is often stored in a volatile memory included in the control device such as a microcomputer. Such information is not expected to remain in a valid form in the memory after the run-down source battery is removed from the camera body for change. When the photo-taking operation is resumed with a new source battery, the load devices of the camera do not function properly since their operations are based on muddled photographic information in the memory.
In order to avoid this inconvenience, it has conventionally been practiced to initialize the control device such as a microcomputer when a source battery is newly loaded into the camera body.
In the camera noted above, the source battery is changed with output of the control signals to the load devices suspended after the detecting device has given a low-voltage detection signal. This is done on the thought that the lowering below the predetermined level of the output voltage of the battery is caused by none other than a capacity reduction of the battery, and that a shortage in the voltage application to the first control device could result in output of abnormal control signals. This conventional practice has the following disadvantages.
The load devices of the camera vary in power consumption. Some, such as the display device and automatic exposure device, involve only minor current variations when in operation, and others, such as the electronic flash and automatic film advancing device, cause a large current flow at an initial stage of operation. There are occasions on which the electronic flash or the automatic film advancing device is operated with the battery capacity having reduced to a certain degree but not entirely exhausted. The output voltage of the battery may then fall below the predetermined level as a result of voltage reduction due to an internal resistance of the battery.
With the camera noted above, however, the first control device is prohibited from outputting the control signals in such a situation. It often is the case that the source battery is changed even if the battery has not run down to the extent to impair normal operations of the load devices and control device. This is a wasteful practice.
Moreover, since the control device is initialized when a new source battery is loaded, the various photographic information must be set all over again and restored in the memory for resuming the photo-taking. The information setting operation is troublesome and time-consuming.